An optical cable typically comprises an optical core incorporating a plurality of optical fibers for the transmission of optical signals and one or more external protective and/or reinforcing layers. The optical core, typically the one suitable for submarine applications, is advantageously of the “tight” type, which comprises a central support element and, around it, one or more layers of polymer material in which the optical fibers are embedded in a fixed position.
The manufacturing of an optical cable including a core of the tight type typically entails at least two steps. The first step relates to the manufacturing of the optical core and comprises the extrusion of at least one polymeric layer, which tightly embeds the optical fibers in a fixed position along a circumference around the central support element. The second step includes, either as a single step or as a plurality of separate steps, the provision of the various types of protecting layers around the optical core.
The manufacturing of a continuous length of an optical cable is generally limited by the maximum continuous manufacturing length of the optical core, which is in turn determined by the length capacity of the devices and apparatuses employed for manufacturing the optical core, e.g. the capacity of the bobbins for feeding the optical fibers. The maximum continuous manufacturing length of an optical core (referred to as a “section” of the optical core in the following) is typically of about 50 km and may arrive up to about 100 km in some particular cases. In addition, due to possible accidents during manufacturing of the optical core (e.g. breakage of the optical fibers), it may happen that even shorter lengths of optical core are produced, which are nevertheless worth to be employed for the manufacturing of an optical cable.
At present, two or more sections of the so produced optical core are then employed for manufacturing respective sections of an optical cable, which sections need then to be assembled together in order to obtain the desired lengths of cable to be installed (e.g. up to 300÷400 km for unrepeatered systems). This post-manufacturing assembling operation, carried out at the end of manufacturing process, is effected by means of a joint box, where the different elements of the optical cable are jointed together and which has generally much greater dimensions with respect to the cable, thus introducing an element of rigidity in the overall cable structure.
A submarine cable joint adapted for jointing ends of an optical submarine cable is disclosed for instance in U.S. Pat. No. 4,784,459.
The applicant has now found a method for jointing different sections of an optical core of the tight type, which method allows to obtain a jointed section having substantially the same diameter as the one of the optical core. The so obtained jointed core thus allows to manufacture substantial lengths of said cable without the need to introduce discontinuity elements in the structure of the cable, such as the jointing boxes.